What it is
On a superconducting quantum processor, Google Quantum AI measured second-order out-of-time-order correlators, and found they remain sensitive to a many-body system's dynamics at long times, where ordinary observables are washed out by scrambling. The measurement reveals constructive interference between Pauli strings that form large loops in configuration space, a signature that also makes the quantity hard to simulate classically.
Why it matters
Probing quantum dynamics past the scrambling wall is a long-standing barrier. A measurable quantity that survives it, and is classically hard, is both a physics tool and a candidate for quantum advantage.
Underlined numbers link to their source. Every metric and quoted figure is listed under Sources and data below.
Filed underquantum simulation, out-of-time-order correlator, superconducting qubits, quantum chaos, quantum advantage
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A short explainer of this result.